1. Field of the Invention
This invention relates to an internal combustion engine ignition device mounted on various vehicles.
2. Description of the Related Art
Internal combustion engine ignition devices (referred to as igniters) of the prior art often have a hybrid IC (HyIC) type configuration in which: an ignition coil driven by a transistor such as an IGBT, and a switching control circuit having a function of controlling energization, outputting the internal state (ignition operation) or the like of the ignition coil, are combined; a one-chip type configuration in which the two are integrated into the same semiconductor chip; or a multi-chip type configuration in which a switching control circuit is formed as an integrated circuit and combined with an IGBT chip.
As configuration examples of an internal circuit of such an igniter, configurations shown in Japanese Patent Application Laid-Open No. H11-201013 (FIG. 1) and Japanese Patent Application Laid-Open No. 2008-2392 (FIG. 2) are known.
As an output function for showing the internal state of an igniter, an example in which a current flowing through a transistor (energization state of an ignition coil) is detected and output will be described using a block diagram in FIG. 11. In this figure, the connections of each of an igniter 1, an electronic control unit 2 (ECU), an ignition coil 3, a spark plug 4, and a power supply battery 5 (VB) are shown.
In the respective terminals of the igniter 1 mentioned above, a ground terminal G is at ground potential (0 V), the voltage of a switching input terminal S is Vs, the voltage of an output terminal F for coil current detection is Vfo, the voltage of a battery terminal B is VB, and a primary current flowing through a coil drive terminal C is Ic. The output terminal F is a terminal for generating the voltage Vfo (a voltage pulse at L level) for determining whether the primary current Ic is flowing steadily.
The igniter 1 is configured of a switching control circuit 11, a sense IGBT 12 which is a coil driving transistor, a resistor 13, a MOSFET 14 which is an F-output transistor, comparators 15 and 16, and an exclusive OR circuit 17. The F-output transistor refers to a transistor for outputting the voltage Vfo from the output terminal F.
FIG. 12 shows voltage and current waveforms of respective parts illustrating the operation of the igniter 1. The operation will roughly be described using FIG. 11 and FIG. 12. The voltage Vs which is a signal voltage instructing to drive the coil is applied to the switching control circuit 11 which operates on the power supply battery 5 by the electronic control unit 2 via the switching input terminal S. Accordingly, the sense IGBT 12 is driven turned on by an output voltage Vg (a gate voltage) output from the switching control circuit 11, causing the primary current Ic to flow through the ignition coil 3.
Since the resistor 13 (which may also be referred to as sense resistor) is connected to a sense terminal 12a of the sense IGBT 12 which outputs a current of several percent or less of the primary current Ic, a sense voltage Vsns is generated. The sense voltage Vsns is compared with reference voltages VH and VL respectively using the comparators 15 and 16.
When the sense voltage Vsns is less than the reference voltage VL, output signals of the comparators 15 and 16 are both at L level, and an output signal of the exclusive OR circuit 17 is at L level. Therefore, the MOSFET 14 which is the F-output transistor is in an off state, and the voltage Vfo of the output terminal F is at H level. In the case where the sense voltage Vsns is between the reference voltage VL and the reference voltage VH, the output signal of the comparator 16 is at H level, and the output signal of the comparator 15 is at L level. Therefore, the output signal of the exclusive OR circuit 17 is at H level, the MOSFET 14 which is the F-output transistor is in an on state, and the voltage Vfo of the output terminal (an F terminal) is at L level. Further, when the sense voltage Vsns exceeds the reference voltage VH, the output signals of the comparators 15 and 16 are both at H level. Therefore, the output signal of the exclusive OR circuit 17 is at L level, the MOSFET 14 returns to an off state, and the voltage Vfo of the output terminal F returns to H level.
During a period in which the primary current Ic is rising, i.e., a period in which the sense voltage Vsns is rising, the voltage pulse at L level is generated in the voltage Vfo of the output terminal F by the MOSFET 14 which is the F-output transistor being turned on, and a voltage at H level is output by the MOSFET 14 being turned off. With this voltage pulse at L level, i.e., by the voltage Vfo of the output terminal F becoming the voltage pulse at L level, the electronic control unit 2 recognizes the generation of the primary current Ic, determines the ignition timing for the igniter 1, and ignites the spark plug.
In order to determine the ignition timing with high precision, a period in which the voltage Vfo of the output terminal F has dropped, i.e., a pulse width W of the voltage pulse at L level, needs to be precise.
The switching control circuit 11 mentioned above has, in addition to a switching control function for the sense IGBT 12, a delay control function for noise reduction, a function of preventing burn of the ignition coil 3 by reducing the level of the output voltage Vg using the sense voltage Vsns to stabilize the primary current Ic (as shown in the waveform in FIG. 12), a timer function by which the application of the voltage Vs is monitored and cut off after a certain period of time has elapsed, or the like. By cutting off the voltage Vs, the spark plug is ignited.
Since the duration of the voltage Vs of the switching input terminal S output from the electronic control unit 2 is controlled upon receiving the voltage pulse of the voltage Vfo of the output terminal F mentioned above, the pulse width W of the voltage pulse of the voltage Vfo of the output terminal F requires high precision in order for the spark plug 4 to be ignited with high precision.
In the case where the sense IGBT 12 is not used and an ordinary IGBT with three terminals (i.e., a collector, emitter, and gate) is used, a similar control is possible by connecting a resistor of low impedance between an emitter terminal and a ground terminal to generate the sense voltage Vsns in a similar manner.
Further, regarding an igniter, Japanese Patent Application Laid-Open No. H1-104980 discloses a method of providing hysteresis at a detection threshold value as a method of preventing malfunction due to noise upon detecting an electrical signal.
As shown in FIG. 11 mentioned above, the internal circuit of the igniter 1 is operated with the ground terminal G as the reference. A transient current of the internal circuit may flow to or from the ground terminal G, such that a transient voltage caused by an impedance component during the current flow causes a fluctuation in a reference potential of the switching control circuit 11, the resistor 13, and the comparators 15 and 16.
The fluctuation in the reference potential is directly superimposed as a noise component also in a signal line in each part of the circuit observed with the ground terminal G as the reference.
A great factor in the fluctuation of the reference voltage is the on-off operation of the MOSFET 14 which is the F-output transistor. When the MOSFET 14 is turned on, a large current flows from a controlled power supply VCC to the ground terminal G via a resistor having a low resistance value of several hundred ohms. Since there are stray inductance and stray capacitance between the controlled power supply VCC and the ground, the MOSFET 14 being turned on or off causes the potential of the ground terminal G to fluctuate and a noise component to be superimposed on the ground potential. With the noise component being superimposed on the ground potential, a waveform of a sense voltage Vsns′ as in FIG. 12 appears. Accordingly, pulse noise in the form of chattering is generated in the output of the comparators 15 and 16 due to a comparing operation of the reference voltages VH and VL.
When the pulse noise in the form of chattering is generated, the pulse noise is transmitted via the exclusive OR circuit 17 and the MOSFET 14 which is the F-output transistor, resulting in a waveform of a voltage Vfo′ of the output terminal as in FIG. 12. Accordingly, pulse noise in the form of chattering is generated in the voltage pulse at L level at falling and rising edges before and after the voltage pulse at L level is output. When the pulse noise is superimposed, the period (pulse width W) in which there has been drop to the voltage pulse at L level (a Low pulse) is narrowed to a pulse width W′. When the voltage pulse with the narrow pulse width W′ is input to the electronic control unit 2, the electronic control unit 2 determines the ignition timing for the igniter 1 erroneously, and the spark plug is not ignited with high precision. That is, an improper determination on the ignition timing by the electronic control unit 2 occurs.
Japanese Patent Application Laid-Open No. H11-201013 (FIG. 1), Japanese Patent Application Laid-Open No. 2008-2392 (FIG. 2), and Japanese Patent Application Laid-Open No. H1-104980 do not describe preventing an improper determination on the ignition timing by using comparing means (a hysteresis comparator) having hysteresis characteristics in an internal combustion engine ignition device in which an on-off control of current for energizing an ignition coil is performed and an output terminal for externally outputting the ignition state is provided, even in the case where noise superimposed at the time of rise of the current flowing through the ignition coil is generated.